DESCRIPTION

Submodules allow foreign repositories to be embedded within
a dedicated subdirectory of the source tree, always pointed
at a particular commit.

They are not to be confused with remotes, which are meant mainly
for branches of the same project; submodules are meant for
different projects you would like to make part of your source tree,
while the history of the two projects still stays completely
independent and you cannot modify the contents of the submodule
from within the main project.
If you want to merge the project histories and want to treat the
aggregated whole as a single project from then on, you may want to
add a remote for the other project and use the subtree merge strategy,
instead of treating the other project as a submodule. Directories
that come from both projects can be cloned and checked out as a whole
if you choose to go that route.

Submodules are composed from a so-called gitlink tree entry
in the main repository that refers to a particular commit object
within the inner repository that is completely separate.
A record in the .gitmodules (see gitmodules(5)) file at the
root of the source tree assigns a logical name to the submodule and
describes the default URL the submodule shall be cloned from.
The logical name can be used for overriding this URL within your
local repository configuration (see submodule init).

This command will manage the tree entries and contents of the
gitmodules file for you, as well as inspect the status of your
submodules and update them.
When adding a new submodule to the tree, the add subcommand
is to be used. However, when pulling a tree containing submodules,
these will not be checked out by default;
the init and update subcommands will maintain submodules
checked out and at appropriate revision in your working tree.
You can briefly inspect the up-to-date status of your submodules
using the status subcommand and get a detailed overview of the
difference between the index and checkouts using the summary
subcommand.

COMMANDS

add

Add the given repository as a submodule at the given path
to the changeset to be committed next to the current
project: the current project is termed the "superproject".

This requires at least one argument: <repository>. The optional
argument <path> is the relative location for the cloned submodule
to exist in the superproject. If <path> is not given, the
"humanish" part of the source repository is used ("repo" for
"/path/to/repo.git" and "foo" for "host.xz:foo/.git").

<repository> is the URL of the new submodule's origin repository.
This may be either an absolute URL, or (if it begins with ./
or ../), the location relative to the superproject's origin
repository (Please note that to specify a repository foo.git
which is located right next to a superproject bar.git, you'll
have to use ../foo.git instead of ./foo.git - as one might expect
when following the rules for relative URLs - because the evaluation
of relative URLs in Git is identical to that of relative directories).
If the superproject doesn't have an origin configured
the superproject is its own authoritative upstream and the current
working directory is used instead.

<path> is the relative location for the cloned submodule to
exist in the superproject. If <path> does not exist, then the
submodule is created by cloning from the named URL. If <path> does
exist and is already a valid git repository, then this is added
to the changeset without cloning. This second form is provided
to ease creating a new submodule from scratch, and presumes
the user will later push the submodule to the given URL.

In either case, the given URL is recorded into .gitmodules for
use by subsequent users cloning the superproject. If the URL is
given relative to the superproject's repository, the presumption
is the superproject and submodule repositories will be kept
together in the same relative location, and only the
superproject's URL needs to be provided: git-submodule will correctly
locate the submodule using the relative URL in .gitmodules.

status

Show the status of the submodules. This will print the SHA-1 of the
currently checked out commit for each submodule, along with the
submodule path and the output of git describe for the
SHA-1. Each SHA-1 will be prefixed with - if the submodule is not
initialized, + if the currently checked out submodule commit
does not match the SHA-1 found in the index of the containing
repository and U if the submodule has merge conflicts.

If --recursive is specified, this command will recurse into nested
submodules, and show their status as well.

If you are only interested in changes of the currently initialized
submodules with respect to the commit recorded in the index or the HEAD,
git-status(1) and git-diff(1) will provide that information
too (and can also report changes to a submodule's work tree).

init

Initialize the submodules, i.e. register each submodule name
and url found in .gitmodules into .git/config.
It will also copy the value of submodule.$name.update into
.git/config.
The key used in .git/config is submodule.$name.url.
This command does not alter existing information in .git/config.
You can then customize the submodule clone URLs in .git/config
for your local setup and proceed to git submodule update;
you can also just use git submodule update --init without
the explicit init step if you do not intend to customize
any submodule locations.

update

Update the registered submodules, i.e. clone missing submodules and
checkout the commit specified in the index of the containing repository.
This will make the submodules HEAD be detached unless --rebase or
--merge is specified or the key submodule.$name.update is set to
rebase, merge or none. none can be overridden by specifying
--checkout.

If the submodule is not yet initialized, and you just want to use the
setting as stored in .gitmodules, you can automatically initialize the
submodule with the --init option.

If --recursive is specified, this command will recurse into the
registered submodules, and update any nested submodules within.

If --force is specified, the submodule will be checked out (using
git checkout --force if appropriate), even if the commit specified in the
index of the containing repository already matches the commit checked out in
the submodule.

summary

Show commit summary between the given commit (defaults to HEAD) and
working tree/index. For a submodule in question, a series of commits
in the submodule between the given super project commit and the
index or working tree (switched by --cached) are shown. If the option
--files is given, show the series of commits in the submodule between
the index of the super project and the working tree of the submodule
(this option doesn't allow to use the --cached option or to provide an
explicit commit).

Using the --submodule=log option with git-diff(1) will provide that
information too.

foreach

Evaluates an arbitrary shell command in each checked out submodule.
The command has access to the variables $name, $path, $sha1 and
$toplevel:
$name is the name of the relevant submodule section in .gitmodules,
$path is the name of the submodule directory relative to the
superproject, $sha1 is the commit as recorded in the superproject,
and $toplevel is the absolute path to the top-level of the superproject.
Any submodules defined in the superproject but not checked out are
ignored by this command. Unless given --quiet, foreach prints the name
of each submodule before evaluating the command.
If --recursive is given, submodules are traversed recursively (i.e.
the given shell command is evaluated in nested submodules as well).
A non-zero return from the command in any submodule causes
the processing to terminate. This can be overridden by adding || :
to the end of the command.

As an example, +git submodule foreach \echo $path `git
rev-parse HEAD`+ will show the path and currently checked out
commit for each submodule.

sync

Synchronizes submodules' remote URL configuration setting
to the value specified in .gitmodules. It will only affect those
submodules which already have a URL entry in .git/config (that is the
case when they are initialized or freshly added). This is useful when
submodule URLs change upstream and you need to update your local
repositories accordingly.

OPTIONS

-q

--quiet

Only print error messages.

-b

--branch

Branch of repository to add as submodule.

-f

--force

This option is only valid for add and update commands.
When running add, allow adding an otherwise ignored submodule path.
When running update, throw away local changes in submodules when
switching to a different commit; and always run a checkout operation
in the submodule, even if the commit listed in the index of the
containing repository matches the commit checked out in the submodule.

--cached

This option is only valid for status and summary commands. These
commands typically use the commit found in the submodule HEAD, but
with this option, the commit stored in the index is used instead.

--files

This option is only valid for the summary command. This command
compares the commit in the index with that in the submodule HEAD
when this option is used.

-n

--summary-limit

This option is only valid for the summary command.
Limit the summary size (number of commits shown in total).
Giving 0 will disable the summary; a negative number means unlimited
(the default). This limit only applies to modified submodules. The
size is always limited to 1 for added/deleted/typechanged submodules.

-N

--no-fetch

This option is only valid for the update command.
Don't fetch new objects from the remote site.

--merge

This option is only valid for the update command.
Merge the commit recorded in the superproject into the current branch
of the submodule. If this option is given, the submodule's HEAD will
not be detached. If a merge failure prevents this process, you will
have to resolve the resulting conflicts within the submodule with the
usual conflict resolution tools.
If the key submodule.$name.update is set to merge, this option is
implicit.

--rebase

This option is only valid for the update command.
Rebase the current branch onto the commit recorded in the
superproject. If this option is given, the submodule's HEAD will not
be detached. If a merge failure prevents this process, you will have
to resolve these failures with git-rebase(1).
If the key submodule.$name.update is set to rebase, this option is
implicit.

--init

This option is only valid for the update command.
Initialize all submodules for which "git submodule init" has not been
called so far before updating.

--reference <repository>

This option is only valid for add and update commands. These
commands sometimes need to clone a remote repository. In this case,
this option will be passed to the git-clone(1) command.

NOTE: Do not use this option unless you have read the note
for git-clone(1)'s --reference and --shared options carefully.

--recursive

This option is only valid for foreach, update and status commands.
Traverse submodules recursively. The operation is performed not
only in the submodules of the current repo, but also
in any nested submodules inside those submodules (and so on).

<path>...

Paths to submodule(s). When specified this will restrict the command
to only operate on the submodules found at the specified paths.
(This argument is required with add).

FILES

When initializing submodules, a .gitmodules file in the top-level directory
of the containing repository is used to find the url of each submodule.
This file should be formatted in the same way as $GIT_DIR/config. The key
to each submodule url is "submodule.$name.url". See gitmodules(5)
for details.